1. Field of the Invention
The present invention relates generally to ink jet printing apparatus, and more particularly relates to the fabrication of piezoelectrically operable ink jet printhead assemblies.
2. Description of Related Art
A piezoelectrically actuated ink jet printhead is a device used to selectively eject tiny ink droplets onto a print medium sheet operatively fed through a printer, in which the printhead is incorporated, to thereby form from the ejected ink droplets selected text and/or graphics on the sheet. In one representative configuration thereof, an ink jet printhead has a horizontally spaced parallel array of internal ink-receiving channels. These internal channels are covered at their front ends by a plate member through which a spaced series of small ink discharge orifices are formed. Each channel opens outwardly through a different one of the spaced orifices.
A spaced series of internal piezoelectric wall portions of the printhead body separate and laterally bound the channels along their lengths. To eject an ink droplet through a selected one of the discharge orifices, the two printhead sidewall portions that laterally bound the channel associated with the selected orifice are piezoelectrically deflected into the channel and then returned to their normal undeflected positions. The driven inward deflection of the opposite channel wall portions increases the pressure of the ink within the channel sufficiently to force a small quantity of ink, in droplet form, outwardly through the discharge orifice.
Under previous methods of constructing piezoelectric ink jet printheads the printhead body section in which the channels are to be formed is first poled, to make it piezoelectrically deflectable or "active", by imposing a predetermined voltage widthwise across the body section in a selected poling direction parallel to the desired piezoelectric deflection direction of the internal sidewall sections to be later created in the poled body section by forming a spaced series of parallel grooves therein. These grooves may be formed using a sawing, laser cutting or etching process.
A typical material used in the formation of piezoelectric ink jet printhead bodies is a piezoceramic material commonly referred to as "PZT." The proper poling of PZT requires voltages on the order of 30 to 75 volts per mil. Accordingly, the widthwise poling of a one inch wide printhead body section formed from PZT requires a poling voltage within the range or from about 30,000 volts to about 75,000 volts.
This poling voltage requirement has resulted in limiting the manufacturable width of a PZT ink jet printhead body, in a direction perpendicular to the ink discharge direction of the printhead, to about one inch since an appreciably wider PZT body section requires unacceptably higher poling voltages. For example, a ten inch wide PZT body section would require a poling voltage somewhere in the range of from about 300,000 volts to about 750,000 volts. Even if this much wider PZT body section could be properly poled at this extremely high voltage, the interior sidewall actuator sections ultimately formed from the poled section would normally exhibit the undesirable tendency to crack when piezoelectrically deflected during operation of the finished printhead.
This PZT printhead body width limitation has resulted in the inability to manufacture piezoelectric ink jet printheads in full page widths--i.e., in the 8.5"-11" width range. This necessitates the shuttling back and forth of a small width piezoelectric printhead across a print medium sheet interiorly traversing the ink jet printer, as opposed to the desirable alternative of forming the printhead in a page wide width which would permit the printhead to remain stationary during the ink jet printing process.
It would thus be desirable to provide methods for fabricating a piezoelectric ink jet printhead in a page wide printing length. It is accordingly an object of the present invention to provide such methods.